Hi Alex,
On Saturday, 2021-03-13 at 18:18:57 -05, Alexander Bulekov wrote:
> For testing, it can be useful to simulate an enormous amount of memory
> (e.g. 2^64 RAM). This adds an MMIO device that acts as sparse memory.
> When something writes a nonzero value to a sparse-mem address, we
> allocate a block of memory. This block is kept around, until all of the
> bytes within the block are zero-ed. The device has a very low priority
I don't see code below that actually checks if a block is zero-ed and
removes it from the hash table, so is this comment correct?
> (so it can be mapped beneath actual RAM, and virtual device MMIO
> regions).
>
> Signed-off-by: Alexander Bulekov <alx...@bu.edu>
> ---
> MAINTAINERS | 1 +
> hw/mem/meson.build | 1 +
> hw/mem/sparse-mem.c | 152 ++++++++++++++++++++++++++++++++++++
> include/hw/mem/sparse-mem.h | 19 +++++
> 4 files changed, 173 insertions(+)
> create mode 100644 hw/mem/sparse-mem.c
> create mode 100644 include/hw/mem/sparse-mem.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f22d83c178..9e3d8b1401 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2618,6 +2618,7 @@ R: Thomas Huth <th...@redhat.com>
> S: Maintained
> F: tests/qtest/fuzz/
> F: scripts/oss-fuzz/
> +F: hw/mem/sparse-mem.c
> F: docs/devel/fuzzing.rst
>
> Register API
> diff --git a/hw/mem/meson.build b/hw/mem/meson.build
> index 0d22f2b572..ef79e04678 100644
> --- a/hw/mem/meson.build
> +++ b/hw/mem/meson.build
> @@ -1,5 +1,6 @@
> mem_ss = ss.source_set()
> mem_ss.add(files('memory-device.c'))
> +mem_ss.add(when: 'CONFIG_FUZZ', if_true: files('sparse-mem.c'))
> mem_ss.add(when: 'CONFIG_DIMM', if_true: files('pc-dimm.c'))
> mem_ss.add(when: 'CONFIG_NPCM7XX', if_true: files('npcm7xx_mc.c'))
> mem_ss.add(when: 'CONFIG_NVDIMM', if_true: files('nvdimm.c'))
> diff --git a/hw/mem/sparse-mem.c b/hw/mem/sparse-mem.c
> new file mode 100644
> index 0000000000..575a287f59
> --- /dev/null
> +++ b/hw/mem/sparse-mem.c
> @@ -0,0 +1,152 @@
> +/*
> + * A sparse memory device. Useful for fuzzing
> + *
> + * Copyright Red Hat Inc., 2021
> + *
> + * Authors:
> + * Alexander Bulekov <alx...@bu.edu>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +
> +#include "exec/address-spaces.h"
> +#include "hw/qdev-properties.h"
> +#include "hw/sysbus.h"
> +#include "qapi/error.h"
> +#include "qemu/units.h"
> +#include "sysemu/qtest.h"
> +#include "hw/mem/sparse-mem.h"
> +
> +#define SPARSE_MEM(obj) OBJECT_CHECK(SparseMemState, (obj), TYPE_SPARSE_MEM)
> +#define SPARSE_BLOCK_SIZE 0x1000
This is assuming a 4K block size, should that be the same as the system
pagesize is? Or will it not matter w.r.t. how this is being consumed?
> +
> +typedef struct SparseMemState {
> + SysBusDevice parent_obj;
> + MemoryRegion mmio;
> + uint64_t baseaddr;
> + uint64_t length;
> + uint64_t size_used;
> + uint64_t maxsize;
> + GHashTable *mapped;
> +} SparseMemState;
> +
> +typedef struct sparse_mem_block {
> + uint8_t data[SPARSE_BLOCK_SIZE];
> +} sparse_mem_block;
> +
> +static uint64_t sparse_mem_read(void *opaque, hwaddr addr, unsigned int size)
> +{
> + printf("SPARSEREAD %lx\n", addr);
Should this printf() be a logging/trace call? Or do you really want it to be
printed all the time? Also seems out of place before the declaration of
the variables.
Thanks,
Darren.
